Sockets : application becomes very slow

can you post some code snippets...

OK, here it comes :

I created as class called 'NavisionHost' :
----------------------------------------------
Imports System.Net.Sockets
Imports System.Text

Public Class NavisionHost
    Const READ_BUFFER_SIZE As Integer = 65536
    Private MyTCPClient As TcpClient
    Private readBuffer(READ_BUFFER_SIZE) As Byte

    Public Sub New(ByVal client As TcpClient)        
        Me.MyTCPClient = client

        ' This starts the asynchronous read thread.  The data will be saved into
        ' readBuffer.        
        ReDim readBuffer(READ_BUFFER_SIZE)
        Me.MyTCPClient.GetStream.BeginRead(readBuffer, 0, READ_BUFFER_SIZE, AddressOf StreamReceiver, Nothing)
    End Sub

    Public Event LineReceived(ByVal sender As NavisionHost, ByVal Data As String)

    Private Sub StreamReceiver(ByVal ar As IAsyncResult)
        Dim BytesRead As Integer
        Dim strMessage As String

        Dim liPosition As Integer = 0

        Try
            ' Ensure that no other threads try to use the stream at the same time.
            SyncLock MyTCPClient.GetStream
                ' Finish asynchronous read into readBuffer and get number of bytes read.
                BytesRead = MyTCPClient.GetStream.EndRead(ar)
            End SyncLock

            ' Convert the byte array the message was saved into, minus one for the
            ' Chr(13).
            If BytesRead > 0 Then
                strMessage = Encoding.ASCII.GetString(readBuffer, 0, BytesRead - 1)
                RaiseEvent LineReceived(Me, strMessage)
            End If

            ' Ensure that no other threads try to use the stream at the same time.
            SyncLock MyTCPClient.GetStream
                ' Start a new asynchronous read into readBuffer.
                MyTCPClient.GetStream.BeginRead(readBuffer, 0, READ_BUFFER_SIZE, AddressOf StreamReceiver, Nothing)
            End SyncLock
        Catch ex As Exception
        End Try
    End Sub
End Class

-----------------------
This class is used on the form that contains the listener :
-----------------------

 Private myTCPlistener As TcpListener
    Private myListenerThread As Threading.Thread = Nothing

'Enable listener
If Not (myListenerThread Is Nothing) Then
   myTCPlistener.Stop()
   myTCPlistener = Nothing
   myListenerThread = Nothing
End If
myListenerThread = New Threading.Thread(AddressOf  DoListen)
myListenerThread.Start()


Private Sub DoListen()        
StartDoListen:      
        Try
            If ucPublicInfo.LoggedOn And Not (ucPublicInfo.connIPAddress Is Nothing) Then
                If Not (myTCPlistener Is Nothing) Then
                    myTCPlistener.Stop()
                    myTCPlistener = Nothing
                End If
                myTCPlistener = New TcpListener(ucPublicInfo.connIPAddress, ucPublicInfo.iPortNum)
                myTCPlistener.Start()
                Do
                    If Not (ucNavisionHost Is Nothing) Then
                        ucNavisionHost = Nothing
                    End If
                    ucNavisionHost = New NavisionHost(myTCPlistener.AcceptTcpClient)

                    ' Create an event handler to allow the UserConnection to communicate
                    ' with the window.
                    AddHandler ucNavisionHost.LineReceived, AddressOf OnLineReceived
                Loop Until False
            End If
        Catch ex As Exception
          GoTo StartDoListen
        End Try
    End Sub

    Private Sub OnLineReceived(ByVal sender As NavisionHost, ByVal psdata As String)
        'In this procedure the received data (string containing XML document) is processed
        '....
    End Sub

Is this sufficient ?

Here is some samples you might want to look at....

https://www.experts-exchange.com/questions/21172715/System-Net-Sockets-Explained-1-2.html

It becomes slow immediately after receiving the data.  I replaced the pocessing of the data with a simple messagebox and it remains slow.  Could it have something to do with the size of the receivebuffer ?

Hi,

I hope this helps, I think I found the reason why it becomes slow but I don't know how to solve this.  
In the event 'streamreceiver' I replaced

If BytesRead > 0 Then
                strMessage = Encoding.ASCII.GetString(readBuffer, 0, BytesRead - 1)
                RaiseEvent LineReceived(Me, strMessage)
End If

with a messagebox, and this messagebox keeps showing on the PDA.  Do I need an endread or something ?

Oops, just a bit too fast.  I have an endread just before the messagebox.  Then why does the message appear again ?

Another bit of information that might help : the first time the event is called, 40 bytes are received, then always 0 (which is normal as there is nothing send)

I found a solution : if bytesread is zero then i perform an exit sub.  This seems to be working for now.  Thanx for your help anyway.